diff --git a/lisp/progmodes/ruby-mode.el b/lisp/progmodes/ruby-mode.el
index 5c8a4025419..0a6ead870a7 100644
--- a/lisp/progmodes/ruby-mode.el
+++ b/lisp/progmodes/ruby-mode.el
@@ -2516,7 +2516,7 @@ A slash character after any of these should begin a regexp."))
      (goto-char (point-min))
      (cl-loop
       while (search-forward-regexp
-             "^\\(?:.*ruby: \\)?\\(?:.*\\.rb\\|-\\):\\([0-9]+\\): \\(.*\\)$"
+             "^\\(?:ruby: \\)?\\(?:.*\\.rb\\|-\\):\\([0-9]+\\): \\(.*\\)$"
              nil t)
       for msg = (match-string 2)
       for (beg . end) = (flymake-diag-region